Internally lubricated elastomers for use in biomedical applications

Abstract: Improved elastomeric materials useful for medical and therapeutic device applications, such as penetrable septa, are described. In one aspect, the materials are deep-cleaned with solvent to significantly lower levels of undesirable organics. In another aspect, internally lubricated elastomer compositions compatible for use in medical and therapeutic device applications are provided. The lubricating fluid is present in the composition from about 0.5% to 50% by weight, and is initially substantially homogeneously dispersed in the elastomer. The fluid can be integrated into the elastomer by a solvent infusion method.

Description: Field of the Invention This invention is in the field of elastomeric materials suitable for use in biomedical applications. In particular, the invention is related to penetrable elastomeric materials for use as septa for injection or withdrawal of fluids employing needle syringes or related fluid withdrawal/injection devices. Background of the Invention There is a continuing need in the medical device field for inexpensive elastomeric materials that combine biocompatibility with desirable elastomer properties such as flexibility, durability, and tear-strength. In particular, improved inexpensive biocompatible elastomer materials for sealing and access applications are needed. The present invention provides means for treating elastomeric material, particularly inexpensive natural and synthetic rubbers, which significantly improves ease of use while decreasing the amount of undesirable organics that are extractable from the elastomer into physiological fluids. The methods provided minimize deterioration of desirable elastomeric properties of the material and instead result in improvement of certain properties. The methods provided are particularly useful for applications to penetrable elastomeric materials including applications of such materials in human infusion systems. One method involves deep cleaning of elastomers employing organic solvents. A second method involves introduction of lubricating fluids into elastomers to give more easily ,penetrable materials. A third method involves infusion of the elastomer with a solution of a lubricating fluid in an organic solvent to give internally-lubricated elastomeric materials having significantly lower levels of extractable organics. In view of the serious concerns today with reducing health care worker contact with patient blood and other body fluids, there have been increasing efforts in the health care industry to improve the integrity of apparatus for the infusion of or withdrawal of fluids from patients. A needle-penetrable barrier functions as the most convenient means for introducing or withdrawing fluids from patient infusion systems. The penetrable barrier or septum allows access to the infusion system while protecting the patient from external contamination and protecting others from contact with potentially dangerous patient body fluids. It is desirable that such barriers allow penetration for fluid access with minimum force of insertion to lessen the danger of either damage to the apparatus or injury to the patient while maintaining a sealed system. Currently, infusion systems are single patient, single use disposable devices intended for relatively short-term use up to several days. The useful lifetime of any septum in the apparatus is decreased by repeated piercing which results in coring, tearing and abrasion of the septum. After repeated use the septum can leak, compromising the integrity of the system, and may release debris into the system. The useful lifetime of infusion apparatus can be increased by employing a septum material that has improved resistance to coring, tearing and abrasion. Septa currently employed in biomedical applications are typically natural rubber synthetic polyisoprene rubber or silicone rubber. These materials are typically difficult to penetrate and display rapid deterioration on repeated piercing with the large gauge needles (18 and 20 gauge) that are used for blood sampling and fluid infusion. The inventor has found that significantly improved elastomeric septa for biomedical applications can be produced by dispersing a lubricating oil, such as a silicone oil or a mineral oil, throughout an elastomeric material, such as a natural or synthetic rubber. The resulting internally lubricated septa display dramatically lowered resistance to penetration with surprisingly improved resistance to deterioration on piercing, improved resealing properties, and improved tearing and coring resistance. In addition, these internally lubricated septa display surprisingly lowered levels of undesirable organic extractables, making them even more attractive for medical device applications. Attempts to improve the resealability of elastomeric sealing members, such as septa, have included: U.S. patent 3,853,129 of Spademan in which non-uniform stress is induced normal to the longitudinal axis of the septum to facilitate resealing; U.S. patent 5,135,489 of Jepson et al. in which axially directed force is applied to reseal a pre-split septum; and U.S. patent 4,954,149 of Fullerman in which a septum having a pre-cut annular injection passage is sealed employing a duckbill seal. Attempts to provide improved materials for penetrable rubber closures have included: U.S. patent 5,082,875 of Tajima et al. which describes synthetic rubber compositions containing high molecular weight polyethylene (HMPE, MW10 6 to 10 9 ) which are said to have good tensile strength and elongation properties; U.S. patent 4,684,672 of Buchanan et al. which relates to high tear-strength natural or synthetic rubber compositions comprising high density polyolefin, a filler and a multi-functional activator to cross-link the rubber and polyolefin; and U.S. patents 4,810,752 and 4,978,714 of Bayan et al. which describe elastomeric compositions with low hardness, low coefficients of friction, and reduced stickiness which provide good barriers to moisture and oxygen. The composition combines a dynamically vulcanized butyl rubber with uncured organopolysiloxane grafted EPDM polymers. The following references may also be considered relevant to the present invention: U.S. patent 4,123,409 of Kaeble describes a thermoplastic sealing material for contact with animal tissue. An elastomeric material with thixotropic properties combining a high molecular weight non-volatile oil in at least a ratio of 1 to 1 with a block copolymer is described. The material is said to be flexible and conformable to the skin and to provide a wetting-type property. Thermoplastic block copolymers having polystyrene end blocks and butadiene or isoprene intermediate blocks are combined with a hydrocarbon oil, e.g., mineral oil, compatible with the intermediate block. Thermoplastic block copolymers having polyalphamethylstyrene end blocks and polydimethylsiloxane intermediate blocks are combined with silicone oil. Molded articles made with these materials are said to combine conformability and flexibility with adherence strength and resistance to tearing. U.S. patent 5,143,963 of Sterling et al. describes elastomeric compositions having fluorocarbon oils, gums or greases dispersed there through. The compositions have fluorocarbon-like surface properties which are said to be advantageous for medical applications, having superior biocompatibility for medical tubing, implants, etc. U.S. patents 4,386,179, and 4,481,323 of Sterling relate to thermoplastic elastomer compositions having a uniformly dispersed (0.1 to 8%, or 0.1 to 12%) polysiloxane or silicone oil throughout the composition. These compositions are said to be useful in medical applications, for example, as inflatable cuffs or balloons in endotracheal devices. Articles made from these materials are said to have a smooth surface, like a silicone polymer, which is less irritating for skin contact. Compositions include hydrocarbon block copolymers, such as styrene-ethylene-butylene-styrene copolymers, to which silicone oil and optionally mineral oil are added. The disclosure discusses the partial migration of the silicone to the surface of the material. Related U.S. patent 4,578,413 also of Sterling describes polymeric tubing composed of the same thermoplastic elastomer compositions useful for medical applications, particularly for tubing with improved flex-life, low spallation in roller-type applications, and decreased debris production. U.S. patent 4,177,182 of Ichikawa et al. relates to polyvinyl chloride resin compositions comprising 100 parts by weight of polyvinyl chloride series resin, 20-80 parts by weight of a plasticizer, and 0.2 to 7 parts by weight of silicone oil. The silicone oil is said to minimize the elution of the plasticizer from the resin. These resins are said to be well adapted for uses in food containers and medical products, particularly for the collection, preservation and administration of physiological solutions. U.S. patent 3,034,509 of Bernstein et al. describes surgical tubing made with a polyethylene to which 0.5 to 1% by weight silicone oil has been added. The silicone oil is said to reduce toxic reaction to the tubing and to inhibit blood coagulation upon contact with the tubing. U.S. patent 2,992,940 of Pace relates to elastomeric flexible cellular materials from polyisocyanates which are treated by external application of silicone oil or by injection of silicone oil into the cellular structure to eliminate internal tack. This invention provides a resealable septum of penetrable elastomeric material, characterised in that the elastomeric material has a lubricating fluid dispersed therethrough. In one aspect, the septum may be of solvent-washed, deep-cleaned elastomeric materials which have significantly lower levels of undesirable extractable organics than untreated elastomers. Solvent-washed elastomers are improved over analogous untreated elastomers for use as penetrable sealing elements in medical devices. Elastomeric materials are placed in an organic solvent for an extended period of time from 1 h to 24 h, but more typically 4 to 8 h, in order to remove residual undesirable organics. Elastomers are then removed from the solvent bath and dried. Solvents useful for elastomer cleaning include methylene chloride, perchlororthylene, and freons, among others. Natural and synthetic rubbers, particularly those that are peroxide-cured, display dramatically improved results in toxicology tests after washing with volatile organic solvents, e.g., methylene chloride. The elastomer compositions provided typically comprise from 0.5% to 50%, and preferably 1% to 15%, by weight of a lubricating fluid initially substantially homogeneously dispersed in the elastomer. The lubricating fluid functions to internally lubricate the elastomer decreasing the internal coefficient of friction and increasing the ease of needle penetration of the material and increasing the durability of the material to repeated penetration. The levels of undesirable organics that are extractable from the internally lubricated elastomer into physiological fluids are also decreased. The internally lubricated elastomers of this invention retain excellent elastomeric properties. A preferred method for making internally lubricated elastomers of this invention is by solvent infusion. The elastomer is contacted with a solution of a lubricating fluid, preferably about 0.5% to 20% by weight, in an organic solvent to allow the lubricating fluid to infuse into the elastomer such that the lubricating fluid becomes substantially homogeneously dispersed there through. After soaking the elastomer in the solution for an extended period of time, from 1 h to 24 h, but typically from about 4 h to 8 h, the elastomer is removed from the solution and the solvent is removed from the elastomer. A treated, infused elastomer contains individual concentrations from 0.5% to 50% of the lubricating oil depending on the type of oil and elastomer used. Solvents that can be used in the infusion method include methylene chloride, perchloroethylene, and freons, among others. Elastomers of this invention include, but are not limited to, natural and synthetic rubbers, polyurethanes, polyolefins, thermoplastic elastomers, silicone rubbers, and fluorocarbon elastomers. Useful lubricating fluids include, but are not limited to, silicone oils, mineral oils, hydrocarbon oils, aromatic oils, vegetable oils and fluorocarbon oils. Preferred elastomer compositions are natural or synthetic rubbers having an initial concentration from 0.5% to 50% silicone oil dispersed there through. The present invention provides, in particular, internally lubricated septa for use in fluid access sites for human infusion apparatus. Natural and synthetic rubber elastomers, particularly synthetic polyisoprene, having silicone oil dispersed there through are preferred. The septa of the present invention made of internally-lubricated elastomers are improved in ease of use, ease of needle penetration, durability to piercing, and have higher resistance to abrasion and coring than septa made of the analogous non-lubricated elastomers. Brief Description of the Drawings Figure 1 is a schematic drawing of a fluid access site with a septum of the present invention. Figure 2 is a schematic drawing of the cut-away view of the fluid access site of Figure 1. Detailed Description of the Invention Elastomers appropriate for use in this invention include natural or synthetic rubbers, polyurethanes, polyolefins, such as grafted EPDM polymers, thermoplastic elastomers such as styrene block copolymers, silicones, and fluorocarbon elastomers. In general, the methods of this invention can be employed with any elastomer that is compatible for use in medical or therapeutic applications. Elastomers, for example, must be capable of withstanding multiple sterilization cycles. Preferable elastomers are those having the hardness, flexibility, tear strength and resealability to needle puncture necessary for use as penetrable seals, membranes or septa. Elastomers appropriate for use as such seals must be capable of forming a oxygen- and water-excluding barrier between an internal fluid environment, such as in an infusion apparatus, and the external environment. Elastomers can be thermoplastic or thermoset elastomers which can be cured or cross-linked by any method known in the art. Natural and synthetic rubbers can be cured by any known method. Those elastomers to which lubricating fluid is added must be dense enough to hold and retain a lubricating fluid to the desired level between 0.5% to 50% without excessive bleeding of oil which would detrimentally affect biocompatibility of the treated elastomer and result in loss of improved elastomer properties. Organic solvents employed in the deep cleaning of elastomers are typically halogenated hydrocarbons. In general, preferred solvents are those that penetrate the elastomer to remove undesired impurities while causing no unacceptable level of detrimental effect to the properties of the elastomer. The solvent should be volatile, such that it can be readily removed from the elastomer after washing. Lubricating fluids of this invention are liquid at room temperature have viscosities in the range of 10 to 10,000 mm 2 s -1 (cs) at room temperature (RT) and include among others silicone oils, mineral oils, hydrocarbon oils, aromatic oils, flurocarbon oils, vegetable oils, and fish oils. It is preferred that the oil itself be biocompatible causing no significant toxic or irritant reaction with human tissue and having no such effect when used in medical devices, particularly in human infusion devices. High purity, ultra-high purity or medical grade lubricating fluids are preferred. The lubricating fluid is chosen to have a chemical composition and molecular weight such that the oil can be readily dispersed into a given elastomer to a desired initial concentration between 0.5% and 50% by weight without extensive oil bleed thereafter during use in devices. Depending on the elastomer, lower molecular weight lubricating fluids generally infuse to a higher concentration into the elastomer than higher molecular weight fluids. The lubricating fluid may have a chemical composition that is compatible or incompatible with the major component in the elastomer. It is preferred to choose the lubricating fluid to minimize the bonding interactions between molecules of the lubricating fluid and the major elastomer component. It is believed that minimizing such interactions by choice of incompatible lubricating fluids improves the internal lubricating properties of the treated elastomer and improves the resealability and durability of the treated elastomers to repeated needle piercings. It may be desirable in some applications to devolatilize the lubricating fluid. The inventor has found that silicone oil lubricated polyisoprene rubber septa prepared by treating polyisoprene No. 100-35, Gardena Rubber Co., Gardena, California, have substantially greater durability to penetration than lubricated septa prepared from other polyisoprenes tested to date. Thus, preferred internally lubricated septa of this invention are the Gardena 100-35 polyisoprene septa infused with silicone oil. Silicone oils employed in the methods and products of this invention are those that are fluid at RT. They include, but not limited to, those that have viscosity between 10 to 10,000 mm 2 s -1 [centistokes (cs)] (RT) or that have molecular weights in the range from 1200 to 62,000. Silicone oils having viscosities in the range of 20 to 100 mm 2 s -1 (cs) (RT) are preferred for preparation of penetrable rubber septa. Silicone oil having viscosity of about 50 mm 2 s -1 (cs) is more preferred for treatment of synthetic isoprene septa. Useful silicone oils include polysiloxanes having lower alkyl groups, aryl groups or both as substitutents. Aryl substitutents include phenyl groups. Lower alkyl substituents include alkyl groups having from one to six carbon atoms, and preferred lower alkyl substitutents are methyl and ethyl groups. Silicone oils having terminal polar groups, such as hydroxy, or amino substitutents or those in which a low percentage, preferably lower than about 10%, of the substituents of the siloxane are such polar substitutents are useful, particularly in combination with natural or synthetic rubbers, so long as the oil retains an essentially non-polar character. Silicone oils having unsaturated substituents, such as vinyl groups, are useful in preparation of lubricated elastomers, as long as cross-linking of the oil with the elastomer is minimized. Preferred silicone oils of this invention are polydimethyl-siloxane, polydimethyldiphenylsiloxane and polydiphenylsiloxane. The choice of siloxane will depend on the application of the treated elastomer, the desired amount of oil infusion and the chemical composition of the elastomer. Different substituted polysiloxanes will be more or less suitable with different elastomers. For example, polydimethylsiloxane was found to be particularly suitable for the preparation of improved synthetic isoprene rubber septa. Suitable mineral oils include those having viscosities in the range of 10 to 10,000 mm 2 s -1 (cs) (RT) obtained from petroleum by separation or refining and can include paraffinic hydrocarbons, olefinic hydrocarbons, aromatic hydrocarbons, and mixtures thereof. The choice of mineral oil for combination with a given elastomer will depend on the chemical composition of the elastomer, the molecular weight of the oil and the desired end product and use. Mineral oils may be combined with any elastomer compatible in biomedical applications but are preferably combined with silicone rubbers. Fluorocarbon fluids having viscosities in the range of 10 to 10,000 mm 2 s -1 (cs) (RT) are suitable for use in this invention and include fluorinated hydrocarbon oils, fluorinated polyethers, and perfluorinated hydrocarbons and perfluorinated polyethers, among others. Fluorocarbon lubricating fluids may be combined with any elastomer compatible in biomedical applications but are preferably combined with fluorocarbon elastomers. Natural oils, such as vegetable and fish oils, can also be used in this invention. Soybean oil, castor oil, corn oil, cotton seed oil, fish oils, deodorized fish oils, cod-liver oil, squalene and any other edible oil are useful as lubricating fluids for elastomers. Vegetable and other natural oils may be combined with any elastomer compatible in biomedical applications. Other lubricating fluids that have been found to produce elastomers with improved ease of penetration and durability to penetration when infused or otherwise combined into elastomers include: glycerin, triglyceride oil and Benzoflex™. Introduction of glycerin, triglyceride oil or Benzoflex™ into natural or synthetic rubbers particularly polyisoprene rubbers, results in improved internally lubricated rubber materials. Lubricated elastomers may optionally include minor amounts of accelerating agents, antioxidants, plasticizers, curing agents, cross-linking agents, and processing aids as well as fillers and pigments, alone or in combination, so long as biocompatibility of the lubricated elastomer is retained and the function of the elastomer is not adversely affected. Preferred treated elastomers of this invention contain less than about 1% by weight of conventional plasticizing agents. Internally lubricated elastomers can be prepared by any method which results in a substantial uniform distribution of the lubricating fluid throughout the elastomer and in which cross-linking of the lubricating fluid to the elastomer components is minimized. Lubricating fluid and elastomer can be physically blended by cutting, kneading or mixing with or without the application of heat. The blending step can be followed by a curing process so long as the lubricating fluid remains substantially free within the elastomer matrix. Internally lubricated elastomers of the present invention are preferably made by a solvent infusion method in which an elastomer is contacted with a solvent solution in which a lubricating fluid is dissolved. The infused elastomer is removed from the solution and residual solvent is thereafter removed from the infused elastomer. The solvent employed for infusion must solubilize a sufficient amount of the lubricating fluid to facilitate the infusion of the lubricating oil into the elastomer matrix. The solvent must be relatively inert to the elastomer material such that there is no unacceptable deterioration of the elastomer due to the solvent during the infusion step. The solvent should be volatile, such that it can be readily removed from the elastomer after the infusion step. It is believed that the solvent functions to expand the elastomer matrix and facilitates infusion of the lubricating fluid into that matrix. During solvent infusion, the elastomer is contacted with the lubricating fluid solution for a sufficient time to allow the lubricating fluid to become substantially homogeneously dispersed throughout the elastomer at an initial level of from 0.5% to 50% by weight of the elastomer, but not to cause unacceptable deteriora-tion of the elastomer material by the solvent. The speed of infusion of lubricating fluid into the elastomer depends on the type of elastomer, its composition and cure, the type and molecular weight of the lubricating fluid, the concentration of the lubricating fluid in the solvent, and the solvent chosen. The parameters of the method can be readily adjusted along with the contact time with the solution by one of ordinary skill in the art without undue experimentation using the guidance provided herein to achieve an initial desired lubricating fluid concentration in the elastomer. The maximum amount of a given lubricating fluid that can be infused into a given elastomer may be less than 50% by weight. In general, lower molecular weight lubricating fluids can be infused into an elastomer to a higher concentration than higher molecular weight lubricating oils. Thus a higher concentration of infused lubricating fluid can be obtained in a given elastomer, if desired, by employing a fluid having a lower molecular weight. A variety of volatile organic solvents and particularly halogenated solvents can be used in the infusion method. Functional solvents include methylene chloride, ethanol and other low molecular weight alcohols, fluorocarbons, freons, and perchloroethylene. The solvent should not cause unacceptable deterioration of the elastomer over the time of exposure to the solvent solution. Methylene chloride is a preferred solvent for infusion of natural or synthetic rubbers with silicone oil. Freshly washed or infused elastomer can be air-dried to remove solvent. To speed drying time, the infused elastomer can be dried at elevated temperature, or by application of a vacuum or both. Drying temperature should be controlled to avoid damage or degradation of the elastomer or the infused lubricating oil. The solvent infusion method described herein results in an internally lubricated elastomer from which lower levels of undesirable organics are extractable into physiological fluids compared to untreated elastomer. It is believed that the solvent infusion treatment removes impurities from the elastomer which are dissolved in the solvent. Contact with the solvent removes undesirable organics, such as residual curing or cross-linking agents, or accelerators, from the elastomer. Currently elastomers are most often cleaned of undesirable residues or impurities using water or aqueous surfactant solutions. These prior art methods effect only a surface cleaning of the elastomer, leaving behind undesirable organics which may later be extracted from the elastomer into physiological fluids. The lubricating fluid is believed to be initially substantially uniformly dispersed in the elastomer employing the methods herein. After infusion or blending, the lubricating fluid may migrate within the elastomer, so that there is a gradient of distribution of fluid in the elastomer. It is known that silicone oils tend to migrate to the surface of the elastomer giving a somewhat enhanced concentration of silicone oil near the surface. Internally lubricated elastomers of this invention and particularly those prepared by the solvent infusion method display significantly improved results in toxicity testing compared to analogous untreated elastomers. Silicone oil infused natural and synthetic rubbers display significantly improved results compared to analogous untreated rubbers in extraction tests. Internally lubricated elastomers of this invention are useful in a number of medical and therapeutic applications as penetrable membranes or septa for infusion devices and like apparatus. Solvent-cleaned and internally lubricated elastomers of this invention can be used to make septa for medical device applications. After treatment, elastomers can be cut or otherwise formed into a desired septum shape. Elastomers may also be formed into the desired shape prior to treatment; however, the increased volume of the elastomer resulting from lubricating fluid infusion must be taken into account. Typically, septa are circular disc elements about 7mm to 10mm (0.3" to 0.4") thick. The thickness of a septum can be varied to adapt to the application and the properties of the elastomer. Septa may be provided with puncture indicators and needle guides, as is known in the art. Natural and synthetic rubbers infused with silicone oil are particularly good candidates for septum application. An exemplary application of an internally lubricated septum is as a septum in a fluid access site in a human infusion device. Figure 1 is a drawing of a fluid access site 20 for a human infusion system comprising a septum of this invention. The drawing shows the placement of the septum (1) in the body of the fluid access site. The access site has a housing (2) mounted on a base (3). The base optionally has slots (4) for receiving straps to allow the site to be strapped or attached to the patient or a support structure. The housing has two tubular arms (5) extending from a body (8) which form a passageway through the housing for flow of fluid through the access site. This passageway is the lumen of the site. The septum (1) provides a penetrable barrier between the external environment and the lumen. The arms (5) are provided with means for connecting to flexible medical tubing (6), for example luer connectors, by which the access site can be connected into a human infusion system such that fluid will pass from one tube through the lumen of the access site into the other tube. The access site housing has two portions: a lower body portion (8) for receiving the septum and a cap portion (7) for holding the septum in sealing position. The cap portion has a circular aperture (11) in its top face. Once the cap portion is in position on the housing lower body, the aperture in the cap portion is completely covered by the septum. The circumference of the aperture in the cap is less than the circumference of the cap and the external face of the septum is exposed to the external environment while the internal face of the septum is in contact with the lumen. The septum forms the barrier between the lumen and the external environment. After the septum is inserted in the body portion, the cap portion is attached over the septum to the lower hollow cylindrical lower body portion. The cap portion can be snapped in place or can be attached to the lower body by an appropriate adhesive. The lower body portion (8) has a septum securing means, such as an indented lip, which contacts the perimeter of the internal face of the septum holding the septum in place against the aperture of the cap and forming a seal therewith. Once the cap portion is in place attached to the lower body portion, the fluid passageway through the body of the access site connecting to the two tubular arms (6) is formed and sealed from the external environment. Figure 2 is a cut-away view of the housing of the fluid access site of Figure 1 showing the relative positions of the septum (1), cap (7) and body (8). The lower body has a lip (13) for holding the septum. When the cap is fixed in position over the body and septum, the septum is slightly compressed and forms a seal between the lumen (12) and the external environment. In operation, the lumen (12) is filled with fluid which can then be accessed by penetrating the septum with a syringe needle. The inventor has discovered that the lifetimes of internally lubricated septa and non-lubricated septa are substantially dependent upon the depth of penetration of a syringe needle through the septum. In order to access fluid, the needle must penetrate through the septum but septum lifetime is substantially lengthened if the penetration depth of the needle is minimized. A uniform needle penetration depth was achieved by employing shielded needles, such as those of B-D Safety-Gard I.V. Hypodermic needles (Trademark, Becton-Dickensen). These hypodermic needles have a cylindrical plastic shield such that the needle is recessed within the shield when the needle is attached to a syringe. The shield has two opposing curved notches at the needle-end which fit against the tubular arms (5) of the fluid access site. The height of the housing above the tubular arm, L in Figure 2, is chosen so that when the shielded syringe is positioned over the housing cap and the opposing curved notches of the shield engage the tubual arms of the housing, the syringe needle minimally penetrates the septum. The use of shielded needles in combination with the housing of Figure 1 allows uniform minimal penetration of the septum and results in a substantially increased septum lifetime. Piercing the septum with the needle of a syringe allows fluid to be withdrawn from or injected into the passageway in the access site and ultimately from the infusion system. If the infusion system is provided, as exemplified in infusion systems in U.S. patents 5,148,811, and 5,022,066, both of Messinger and 4,981,140 of Wyatt, which are herein incorporated by reference in their entirety, with a means for drawing a patient's blood into the infusion system and into the lumen of the access site, a blood sample can be taken through the septum in the access site. Similarly, medication, additional nutrients and other fluids can be introduced into the infusion system through the septum in the access site. The access site of Figure 1 is only one example of the possible uses of the septa of this invention. In general the septa of this invention can be employed in any medical or therapeutic device application requiring a penetrable seal and particularly in applications for disposable devices or apparatus in which the penetrable seal need not be in extended contact, not over about 72 hours, with tissue or body fluids. EXAMPLES Example 1: Infusion of Isoprene Rubber with Silicone Oil Polyisoprene rubber septa (about 85 g, Product No. 100-35, Gardena Rubber Co., Gardena, California) were placed in about 750 ml of a shaken 10% (V/V) solution of silicone oil in methylene chloride. Silicone oil solutions that are discolored, cloudy or contain black debris particles are unacceptable for use and should be discarded. Septa were soaked for at least 1 hour, but not more than 24 hours. The soaking time is limited in order to avoid deterioration of the septum material by the solvent. After soaking, the septa were removed from the solvent solution. Methylene chloride was then removed from the septa. The septa were either dried at room temperature for at least 24 h. or dried for about 24 h. on trays in an oven at about 60°C. Dependant on the molecular weight of the silicone oil used, from 0.5% to 15% by weight of silicone oil could be infused into polyisoprene septa using this solvent infusion method. Example 2: Septum Comparison Tests Test fluid access sites containing test septa are constructed and subjected to one sterilization cycle. The test sites are then connected with tubing into a single hydraulic circuit. The tubing and injection site passageways are filled with a saline solution, bubbles are removed from the system, and the fluid system is pressurized to check for leaks. Any leaking sites are replaced or adjusted. Durability of septa is tested by repeated punctures of each septum with a syringe and needle. A new needle is employed for each septum puncture. The time between consecutive punctures of a septum is at least 30 m. Shielded hypodermic needles (B-D Safety-Gard I.V. [Trademark] Becton-Dickensen Co.) are employed so that the needle penetrates through the septum to the same extent on every puncture. After each puncture, the septum is observed for leaks and other indicia of deterioration. In addition, after each puncture the needle is examined for obstruction of flow which indicates coring of the septum. Observation of a leak is scored as a septum failure. In addition, if obstruction of a needle is observed on two consecutive punctures of the same septum, that septum fails. After the desired number of punctures have been performed, the access sites can be disassembled and the internal face of the septum can be examined for excessive cracking, splitting or any other failure. Synthetic polyisoprene rubber septa infused with a methylene chloride solution of silicone oil (50 mm 2 s -1 [cs]) as described in Example 1, on average, will show significantly better performance in this durability test than analogous untreated polyisoprene rubber septa. Natural rubber septa infused with a methylene chloride solution of silicone oil (50 mm 2 s -1 [cs]) as described in Example 1, on average, will show significantly better performance in this durability test than analogous untreated natural rubber septa. Natural rubber and synthetic polyisoprene rubber septa infused with silicone oil as described in Example 1 display significantly lower levels of physiological fluid-extractable materials than analogous untreated rubber septa. Silicone-infused rubber septa of this invention display significantly improved properties compared to untreated rubber when subjected to a variety of toxicology tests.

Claims: A resealable septum of penetrable elastomeric material, characterized in that the elastomeric material has a lubricating fluid dispersed therethrough. The septum of claim 1, characterized in that the elastomeric material is a polyurethane, or a polyolefin, or a thermoplastic elastomer, or a silicone elastomer, or a natural or synthetic rubber, preferably a peroxide-cured polyisoprene synthetic rubber. The septum of either of claims 1 and 2, characterized in that the lubricating fluid is a mineral oil, or a fluorocarbon oil, grease or gum. The septum of either of claims 1 and 2, characterized in that the lubricating fluid is a silicone oil, preferably a polydiphenylsiloxane or polydimethylsiloxane. The septum of any one of claims 1 to 4, characterized in that the elastomer is a sulphur-cured polyisoprene synthetic rubber. The septum of any one of claims 1 to 5, characterized in that the lubricating fluid is present at a level of 0.5% to 50% by weight, preferably at a level of 1% to 15% by weight. The septum of any one of claims 1 to 6, characterized in that the lubricating fluid has an average molecular weight of from 1,200 to 62,000. The septum of any one of claims 1 to 7, characterised in that the lubricating fluid has a viscosity of 20 to 100 mm 2 S -1 (cs) preferably 50 mm 2 S -1 (cs). A human infusion apparatus having a fluid access site, characterised in that the fluid access site comprises the septum of any of claims 1 to 8. The septum of any of claims 1 to 8, characterised in that the elastomer is a solvent cleaned elastomer.

Inventors: SMITH III HUBERT S, SMITH III, HUBERT S.
Applicants: COBE LAB, COBE LABORATORIES, INC.
Application year: 1994
Main classification: A61L31
IPC codes: C08L23, A61L29, C08L75, C08L21, A61L31, C08L83, A61L15, A61M39, C08K5